Determination of optical properties using improved frequency-resolved spectroscopy

摘要

Recently, much efforts and progress have been made in using steady state, time-domain and frequency-domain NIR technique to obtain tissue optical properties. We have developed a novel PMS system which can efficiently eliminate the phase-amplitude cross-talk along with a new algorithm to calculate $mu$-a$/ and $mu$-s$/$PRM of strong scattering media we measured. The PMS system consists of two master oscillators separated by a frequency at 25 khz. The two laser diodes (780 and 816 nm) are time shared by a small mirror excited by a 60 Hz chopper so that the phase detector can alternatively detects the response of the object in two wavelength. The output from phase meter is selected by an electronic switch, then filtered, amplified and sent to a computer. In order to eliminate phase-amplitude cross-talk, we designed a dynode feedback control circuit. Its purpose is to keep the amplitude signal from PMT to be constant so that the amplitude has less contribute to the phase shift. At the same time, phase output is corrected using a linear compensation circuit to eliminate the phase shift caused by the high voltage change. The optical bench tests showed the phase-amplitude cross-talk has been reduced to be very small. We did a series model experiments including ink, Introlipid and blood model to test the system. The results show very reasonable $mu$-a$/ and $mu$-s$/$PRM based on photon diffusion equations and algorithm. Next work is to apply it in clinic and measure the hemoglobin saturation change in tissues.